Ring communication systems in which the ring comprises distribution panels or wiring boxes for inserting or bypassing extension lobes (connection lines for extending the ring) are well known, e.g. from the publication by W. Bux et al. "A Local-Area Communication Network Based on a Reliable Token-Ring System", published in "Local Computer Networks", North Holland Publishing Co., 1982, pp 69-82, from U.S. Pat. No. 4,417,242, from European patent application No. 0,082,889, and from the Standards IEEE-802.V and ECMA-89 for token ring systems. In such ring communication systems, one station can be connected to each extension lobe, e.g. through a wall outlet at a remote end of the lobe. When the station is powered up, it sends a DC current as insertion request to the distribution panel (wiring box) which then changes the switch settings for the respective extension lobe from BYPASS to INSERTED, thus incorporating the extension line plus the station (or more exactly its adapter) into the main ring.
These known systems operate well for attaching a single station to each extension lobe. In certain situations, there will be a need for attaching a group of stations to a single wall outlet of a ring communication system, and to place at least some of these stations in a more remote location where no wall outlet exists, connecting each one by an additional cable to the basic extension lobe.
The individual insertion of the stations of such groups plus their additional cables into the main ring will be difficult if the principle of DC signaling as insertion request is to be maintained. Placing a normal basic distribution panel instead of a wall plug at the end of a basic extension lobe to enable the attachment of several stations or branch lines will not be possible because the DC signal path which is a phantom circuit using the two wire pairs of an extension lobe would be interrupted at such normal distribution panel. Furthermore, no DC power would be available at the location of a wall outlet which was replaced by a normal distribution panel so that sending a DC signal as an insertion request from the intermediate location (original place of wall outlet) to the basic distribution panel in the main ring is not possible.
Two solutions were suggested for attaching a group of stations to a single wall outlet in a ring communication system. An article "Loop Cabling System" by F. Almquist et al., IBM Technical Disclosure Bulletin, Vol. 24, No. 9, Feb. 1982, pp. 4818-4820 discloses an arrangement for connecting a complete subloop with several station connectors between two outlets of a basic distribution panel (wiring connection box). This arrangement, however, does not provide for the automatic insertion of a station and its subloop into the ring under remote control by a DC signal from said station so that the usual standard technique for automatic insertion caused by DC signaling would have to be changed. An article "Local Area Station Network Connector" by E.J. Annunciata et al., IBM Technical Disclosure Bulletin, Vol. 27, No. 2, July 1984, pp. 953-955 also disclosed an arrangement in which several stations are attached to a single outlet of a distribution panel (wiring concentrator). This arrangement requires, if DC signaling from the station for insertion control is to be maintained, the provision of particular (bistable) relays which may not be desirable, and further provides the connection of all stations of the group to a wall outlet by a common additional line and not by separate individual lines which may also not be desirable.